Painless Docker - 2nd Edition

What is Docker Swarm?

Docker Swarm is the container orchestration platform developed and maintained by Docker, Inc.

It's specifically designed to simplify the deployment, management, and scalability of containerized applications at scale. Swarm allows users to create and manage a cluster of Docker hosts as a single virtual system - a feature referred to as container orchestration. This makes it easier to distribute containerized applications across multiple nodes.

Docker Swarm comes with key features such as service discovery, load balancing, scaling, rolling updates, high availability, security, integration with Docker, and more.

Service Abstraction

Docker Swarm introduced the concept of services, which represent a group of containers that perform the same task.

When you work with a standalone container, you can use the docker run command to start it. However, when you work with a service, you use the docker service create command to specify the desired state of the service. This transition from transactional to declarative commands is a key feature of Docker Swarm.

With a service, you can define the desired number of replicas, and Docker Swarm ensures that the specified number of containers are running across the cluster. If one of the containers in a service fails, Docker Swarm automatically restarts it to match the desired state.

Load Balancing

Swarm includes an integrated load balancer that distributes incoming requests across containers within a service. This load balancer runs on every node in the cluster and ensures that requests are routed to the appropriate containers, regardless of which node they are running on.